Arrangement for the mechanical interfacing of a MEMS micromotor with a clock wheel and timepiece comprising this arrangement

ABSTRACT

The invention proposes an arrangement for the mechanical interfacing of a micromotor of the MEMS type with a toothed wheel in which the micromotor is produced in the upper layer of a plate made of crystalline or amorphous material and comprises at least one actuator which drives a rotor in rotation, characterised in that a pinion, coaxial with the rotor and arranged above the rotor, is connected in rotation to the rotor by means of at least one pin which is received in an associated housing and in that the pinion meshes with the toothed wheel.

This application claims priority from European Patent Application No.06123972.9, filed Nov. 13, 2006, the entire disclosure of which isincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to an arrangement for the mechanicalinterfacing of a micromotor with a wheel and a timepiece comprising thisarrangement.

The invention relates more particularly to an arrangement for themechanical interfacing of a micromotor of the MEMS type with a toothedwheel in which the micromotor is produced in the upper layer of a platemade of crystalline or amorphous material and comprises at least oneactuator which drives a rotor in rotation.

BACKGROUND OF THE INVENTION

In silicon microactuators, one means of converting electrostatic energyinto work is to dispose structures “as a comb”, formed respectively bymoveable and fixed fingers and set at two different potentials. Themoveable fingers are attached to the combs, themselves attached to anacelle guided linearly by springs. These actuators are produced byphotolithography and dry plasma attack of monocrystalline silicon layershaving a thickness typically of 50 to more than 200 microns.

In order to make a clock wheel turn, it is necessary to convert thelinear movement into rotational movement, via a ratchet system forexample, as in the case of Accutron watches by Bulova (USA), Mosaba byETA or via a hysteresis system such as described in the document WO2004/081695. The linear movement on silicon being of the order of a fewtens of microns, the ratchet driven by the pawls must have teeth ofequivalent dimensions. In order to ensure reliable meshing, thepositioning of this ratchet relative to the moveable fingers must bywithin tolerances which are much lower than the some tens of micronsmentioned earlier.

In order to produce such a mechanical interfacing between the linearmovement of a pawl actuator and the rotational movement, the document WO2006/024651 proposes using microactuators which drive, by means of atooth in a hysteresis movement, a micromanufactured wheel with verysmall teeth, which is coaxial and integral with a clock pinion. Thissolution implies an adjustment of the microactuators relative to thewheel for each assembled piece because the radial positioning toleranceof one mechanism axle, for example a plain bearing made of steel onruby, is of the order of 40 microns. One solution can be to integrate aspring system on the MEMS in order to take up the positioning clearance,such as a bending mechanism of the ratchets, which is proposed in thedocument WO 2006/97516. The positioning is therefore ensured but thepawls or any other mechanism made of silicon therefore protrude directlyon the side of the chip which makes manipulation during assembly moredifficult and also its exposure to dust more direct.

The invention aims to resolve these problems by proposing an arrangementin which the microactuator drives a silicon rotor positioned on the samesubstrate as the microactuator. The invention aims to make themicromotor and the mechanism independent at the level of their radialclearances (radial play), whilst allowing transmission of the puretorque from one to the other.

SUMMARY OF THE INVENTION

To this end, the invention proposes an arrangement of the type mentionedpreviously, characterised in that a pinion, coaxial with the rotor andarranged above the rotor, is connected in rotation to the rotor by meansof at least one pin which is received in an associated hole/slot and inthat the pinion meshes with the toothed wheel.

According to other features of the invention:

-   -   the rotor comprises a plurality of holes/slots that are        distributed angularly in a regular manner about the axis of        rotation of the rotor, and the pins are integral with the        pinion;    -   the pins are produced in a single piece with the pinion;    -   each pin is received in the associated hole/slot with a radial        functioning clearance (radial play) and a circumferential        functioning clearance (circumferential play) determined by        design, wherein the radial clearance (radial play) is provided        by clearance between surfaces forming the plurality of holes in        the rotor and the off-set pins of the pinion;    -   the upper layer of the plate comprises at least one support        surface orientated towards the top of the plate, and the pinion        is provided to abut against this surface when an axial force        orientated towards the bottom of the plate is applied to the        pinion;    -   the rotor is guided in rotation by a shaft mounted in the plate;    -   the rotor is guided in rotation by the same shaft as the pinion;    -   the pinion meshes with the wheel in a meshing zone situated        close to an exterior circumferential edge of the plate;    -   the rotor is driven in rotation by the actuator by means of a        pawl, and the ratcheting zone is offset angularly relative to        the meshing zone.

The invention also proposes a timepiece which comprises an arrangementaccording to one of the preceding features for the mechanicalinterfacing of a wheel of a gear-train of the timepiece with amicromotor of the timepiece.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the present invention will appear moreclearly upon reading the following detailed description, with referenceto the annexed drawings which are given by way of non-limiting exampleand in which:

FIG. 1 is a sectional view in which represents schematically a timepieceproduced according to the teachings of the invention;

FIG. 2 is a perspective view which partially represents the movement ofthe timepiece of FIG. 1, equipped with a driving module comprising aMEMS micromotor;

FIG. 3 is a view from above which represents schematically the drivingmodule of FIG. 2;

FIG. 4 is an exploded perspective view which represents the drivingmodule of FIG. 2 and the casing which surrounds this driving module;

FIG. 5 is an enlarged view in axial section according to the plane 5-5which represents schematically a portion of the driving module and whichillustrates the rotational assembly of a pinion and of a rotor of themicromotor about a shaft;

FIG. 6 is a schematic view in axial section according to the plane X′Xwhich illustrates the driving of the pinion by the rotor by means ofpins;

FIG. 7 is schematic view from above which illustrates the driving of thepinion by the rotor by means of pins;

FIG. 8 is a schematic view in axial section according to the plane X′Xwhich illustrates a variant of the assembly of the shaft relative to therotor;

FIG. 9 is a view from below which represents schematically the elasticfixing structures which are provided in the plate for clamping andcentring the shaft according to the assembly of FIG. 8;

FIG. 10 is a view from above which represents schematically a siliconwafer and which illustrates an example of the arrangement of a pluralityof micromotors on the wafer.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS

In FIG. 1, a timepiece 10 is represented schematically, comprising awristwatch equipped with a driving module 13 according to the teachingsof the invention, the driving module 13 being arranged here inside acasing 12.

The timepiece 10 comprises a watch casing 14 closed by a crystal 16, adial 18 and analogical display means here comprising hands 20. The hands20 are provided in order to be driven in rotation by the driving module13 according to the invention, via a gear-train 22 comprising forexample reduction means. The driving module 13 is supplied withelectrical energy by a battery 24. The casing 12, the driving module 13,the gear-train 22 and the battery 24 are mounted here on a plate 26 andtogether form the movement 27 of the timepiece 10, this movement 27being fixed inside the watch casing 14. Of course, the movement 27comprises other elements (not represented), in particular an electronicmodule comprising an integrated circuit, a time base comprising aquartz, a printed circuit board etc.

In FIG. 2, a part of the movement 27 of the timepiece 10, in particularthe plate 26, is represented, on which the casing 12 and the gear-train22 are mounted.

The driving module 13 is intended to mesh with a timepiece wheel, termedinput wheel 28 of the gear-train 22.

The various elements of the driving module 13 according to the inventionare represented in more detail in FIGS. 3 to 7.

The driving module 13 comprises a plate 30 made of crystalline oramorphous material, for example silicon, comprising a lower layer whichforms a substrate 32 and an upper layer 34 in which a micromotor 36 ofthe MEMS type (Micro Electro Mechanical System) is etched. Themicromotor 36 is formed here by two actuators 38, 40 which drive a rotor42 which is etched in the upper layer 34 in rotation.

Each actuator 38, 40 comprises a stylus 44, 46, moveable following adirection A1, A2 parallel to the plane of the plate 30. Each stylus 44,46 is provided, on its free end, with a pawl 48, 50 which is provided tocooperate with a ratchet toothing 52 provided on the exteriorcircumferential edge of the rotor 42 in order to drive it in rotationsequentially.

Preferably, each stylus 44, 46 extends following a direction A1, A2which cuts the associated actuator 38, 40 in two overall symmetricalparts.

Preferably, a first actuator 38 comprises a thrust pawl 48 and a secondactuator 40 comprises a traction pawl 50.

Each actuator 38, 40 is of the electrostatic type with interdigitedcombs and produced by etching in the silicon plate 30. The plate 30 hereis of the Silicon On Insulator (SOI) type and comprises a thick lowerlayer 32 of the silicon substrate, an intermediate layer 54 of siliconoxide and an upper layer 34 made of silicon of a lesser thickness thanthe substrate 32.

The fixed part of each actuator 38, 40 comprises a supply pad 56, 58provided to be connected electrically to the electronic module, and themoveable part of each actuator 38, 40 comprises a contact pad 57, 59which places these moveable parts at a predetermined potential, here atzero volts.

A micromotor comprising electrostatic actuators produced in a siliconplate is described and represented for example in the document WO2004/081695, incorporated here by reference. In this document, the motoris produced by etching in a silicon layer. It comprises a tootheddriving wheel and actuating fingers which cooperate with the teeth ofthe wheel in order to induce its rotation. Each actuating finger isintegral in displacement with a moveable comb which is displacedrelative to a fixed comb as a function of a voltage applied to the fixedcomb.

An embodiment using an SOI plate is described with reference to FIGS. 7Ato 7D in the document mentioned above.

According to an advantageous embodiment, each actuator 38, 40 isassociated with a passive pawl 49, 51, the ratcheting zone of which issituated between the meshing zone 70 and the ratcheting zone of theassociated ratchet. These passive pawls 49, 51 are maintainedelastically meshed with the rotor 42 in order to ensure precise angularpositioning, in particular in the course of the driving phases, when theother pawls 48, 50 are displaced.

According to the embodiment represented in FIGS. 3 to 7, the rotor 42 isguided by a central plain bearing 60 which is integrated or inserted,produced at the same time as the pawls 48, 50 and having diametricclearance (play) of between 4 and 10 microns, the approximate lowerlimit corresponding to a silicon layer thickness of 80 microns. Thepawls 48, 50 will function well if they act on a tangential course whichis significantly greater than this clearance (play), i.e. typicallybetween 20 and 100 microns. This corresponds well to the range ofpossible courses with guidance of the styli 44, 46 by deflecting springs(not shown).

The torque of the rotor 42 is transmitted to a pinion 62 by a systemsimilar to a crank. The pinion 62 situated just above the rotor 42 iscoaxial with the latter and it is guided by a central shaft 64 defininga central axis (axis z′z) along the shaft. The pinion 62 is providedwith pins 66 which are engaged in the slots 68 of the rotor 42.Operating clearances (play) j_group, j_rot, j_pi are provided betweenthe various elements of the rotor 42 and of the pinion 62 as representedin the diagram of FIG. 7. Thus rotor 42 and pinion 62 are coupled inrotation angularly and they move independently in a radial directionwith respect to the axis z′z: the clearances (play) in the plane xy aretaken up by the bearing 60 for the rotor 42 and by the shaft 64 for thepinion 62. Hence the radial reaction force due to the load is not takenup by the bearing 60 at the level of the rotor 42 but by the guidance ofthe pinion 62 by the shaft 64. Therefore, the micromanufactured elementsof the micromotor 36 are protected from larger forces exerted by thetimepiece elements, in the case of impacts for example.

The pinion 62 is provided in order to mesh with the input wheel 28 ofthe mechanism 22 in a meshing zone 70 situated near to an exteriorcircumferential edge 72 of the plate 30.

According to an advantageous feature, the rotor 42 is provided on theplate 30 in order to minimise the distance D between the toothing 52 ofthe rotor 42 and the exterior circumferential edge 72 of the plate 30corresponding to the meshing zone 70. Furthermore, the exterior diameterof the pinion 62 is slightly greater than that of the rotor 42 in orderto project relative to the plate 30 in the meshing zone 70.

In order to simplify the diagram of FIG. 7, a rotor 42 is represented,comprising merely four slots/holes 68 and a pinion 62, which comprisesonly four pins 66, wherein each hole of the plurality of holes has alength (L) and a width (W), wherein the length (L) is greater than thewidth (W), and the length (L) is oriented in a radial direction withrespect to the axis z′z of the central shaft. According to anadvantageous embodiment, such as illustrated in particular by FIGS. 3and 4, eight slots/holes 68 and eight pins 66 are provided.

According to a preferred embodiment, the angular position of theratcheting zone of each pawl 48, 50 with the rotor 42 is offsetangularly relative to the meshing zone 70. The ratcheting zone of eachpawl 48, 50 forms an angle β with the axis x′x. α represents the angle,at a given moment, between the radius passing through the pin 66 whichabuts, in engagement, against the edge of its slot 68/hole, and the axisx′x (FIG. 7).

Then, a judicious choice of all the parameters {α, β, j_rot, j_pi,j_group} for the given radii of pinion 62, rotor 42 and the circle ofpins 66 will assist the efficiency of the transmission of mechanicalenergy from the rotor 42 to the pinion 62. Hence for a particular caseof the invention having β=45°, if the clearances (play) are welladjusted, the efficiency for a system with four pins approaches 85%,which improves the efficiency relative to a case where the rotor 42 andthe pinion 62 are glued one to the other. In fact, in this latter case,all the load would be in the form of lateral silicon-silicon friction atthe level of the bearing 60, and vertical between the circumference ofthe rotor 42 and the substrate 32 because of the pivoting torque.However the silicon-silicon friction is somewhat unfavourable, with drystatic coefficients approaching 0.4.

This transmission solution makes it possible again to vary the diameterof the pinion 62 in order to adapt the torques and the speeds, accordingto the loads. Moreover if the pinion 62 is large enough and protrudesbeyond the circumferential edge 72 of the plate 30, the meshing via thecut is found to be simplified, and the driving module 13 can beassembled on the plate 26 of the timepiece 10 in a modular manner, i.e.without dismantling/reassembling the driven wheel 28.

According to various variants:

-   -   the rotor 42 is micromanufactured in place, and on the same        substrate 32 as the actuators 38, 40 in order to ensure matching        to the bearing 60 and to the pawls;    -   another variant comprises manufacturing a rotor 42 separately,        on the same wafer or on another wafer, this rotor 42 being then        assembled on the plate 30 or stator. This allows a reduction in        the radial clearance (radial play) if desired in the case where        the rotor is guided by the bearing 60;    -   a family of variants is formed by the rotors 42 and/or the        pinions 62 which are micromanufactured by methods other than        DRIE machining (laser cutting, EDM, LIGA, microinjection, etc.)        then assembled on the plate 30 to the stator;    -   another family of variants is formed by pins 66 formed by a        second photolithographic level in the pinion 62 and/or in the        rotor 42.

The driving module 13 according to the invention allows increasedmodularity for adaptation to the load, by allowing the use of pinions 62of various diameters, without modifying the rest of the module 13. Thusan increased modularity is also obtained for the assembly because themechanical interface for the connection to the timepiece gear-train 22is already present thanks to the presence of the pinion 62, integratedinto the driving module 13 and connected in rotation to the micromotor36.

The pinion 62 can be produced in metal such as brass, with pinsconnected pins 66 also produced in metal. The pinion 62 can also beproduced in a single piece with the pins 66 by moulding in plasticmaterial. Production of the pinion 62 in plastic material with metallicpins 66 which are moulded on is also conceivable.

According to the embodiment represented in particular in FIGS. 4 and 5,the axis of rotation z′z of the pinion 62 is formed by a stepped shaft64 made of profil-turned metal which is inserted into the plate 30through a first hole 74 produced in the substrate 32 and which is driveninto a second hole 76 produced in a plate 106 of the casing 12. In thisembodiment, the radial forces applied on the shaft 64 are taken up bythe plate 106.

The shaft 64 comprises a lower end section 78 which, with a lowerintermediate section 80, delimits a first shoulder surface 82 orientatedtowards the top and coming to abut axially against the lower face of theplate 30. The lower intermediate section 80 has a diameter substantiallyequal to the diameter of the first hole 74 and extends into this hole74. The shaft comprises an upper intermediate section 84 of a slightlylesser diameter than the lower intermediate adjacent section 80 andwhich extends into the boring 86 of the pinion 62 in order to guide itin rotation. The upper intermediate section 84 delimits, with the upperend section 88, a second shoulder surface 90 against which a fixing ring92 is maintained axially abutting, said fixing ring being driven ontothe upper end section 88.

As the rotational guidance of the rotor 42 is produced by the bearing 60which is produced by a photolithographic etching process in the samemanner as the first hole 74 which determines the centring of the shaft64 relative to the bearing 60, very good centring of the shaft 64, ofthe pinion 62, of the bearing 60 and of the rotor 42 is obtained.

Furthermore, the lower face of the pinion 62 comprises, opposite thebearing 60, a bulge 94 which prevents the pinion 62 from coming to abutaxially against the rotor 42, in particular in the case of pivoting,which avoids impairment of the rotor 42.

In FIGS. 8 and 9 there is represented another advantageous embodiment inwhich the shaft 64 is mounted in the plate 30 in the manner of aforce-fit by means of elastic fixing structures 96 provided in thesubstrate 32 around the first hole 74. In this embodiment, the radialforces applied on the shaft 64 are taken up by the substrate 32 andtherefore by the elastic fixing structures 96.

The elastic fixing structures 96 are formed here by flexible blades 98which are formed by lithography in the rear face of the plate 30. Thelithography of the front face, for the upper layer 34 comprising thepawls 48, 50 and the rotor 42, likewise being aligned and centred veryprecisely relative to the lithography of the rear face (error less then1 micron) and the result is more precise guidance and centring than withan axle produced in a single piece with the plate 30, since the radialclearance (radial play) can likewise be reduced to 1 micron.

Thanks to this precise alignment and this centring, it is possible todispense with the bearing 60 such that the rotor 42 is then guided inrotation directly by the shaft 64. Thus the shaft 64 can guide inrotation, at the same time, the rotor 42 and the pinion 62. As the shaft64 is produced by profil-turning, which makes it possible to obtain verylimited manufacturing tolerances, a very precise assembly is obtained,which ensures in particular reliable functioning of the actuators 38,40. The rotor 42 is then guided by the external axial wall of the shaft64.

The shaft 64 can finally be fixed in the plate 30 by a complementaryfixing means, for example by welding to the substrate 32 by means of awelding seam 99 which is represented in FIG. 8, or even by glueing.

The problems of friction against the shaft 64 can be resolved bydeposition of a solid thin layer on the external axial wall of the shaft64 which makes it possible to reduce the friction between the parts.

The elastic fixing structures 96 can be chosen in particular from theexamples described and represented in the document CH 695 395 or fromother structures which can ensure precise centring and clamping of theshaft 64 on the plate 30, for example structures formed by flexibletongues with free ends.

Advantageously, considering in particular FIG. 3, the actuators 38, 40describe together an angle of approx. ninety degrees, the bisector ofthis angle passing through the meshing zone 70 and through the axis ofrotation z′z of the rotor 42 such that the driving module 13 has ageneral “V” shape which is defined by the exterior contour of the plate30, this contour being optimised.

The plate 30 comprises a central portion 100 which carries the rotor 42and two lateral portions 102, 104. The exterior contour of the plate 30corresponds overall to the intersection of two rectangles which togetherare orthogonal and which form the two lateral portions 102, 104, with atransverse rectangle which forms the central portion 100, the transverserectangle describing an angle of forty-five degrees relative to each ofthe two other rectangles. The major part of the surface of each lateralportion 102, 104 is occupied by an actuator 38, 40 whilst the major partof the surface of the central portion 100 is occupied by the rotor 42.The meshing zone 70 is provided near to one of the circumferential edges72 of the central portion 100.

Preferably, the regions 56, 57, 58, 59 are arranged on the centralportion 100, on the opposite side from the meshing zone 70 relative tothe axis z′z of the rotor 42.

It can be seen that the “V” shape of the driving module 13 has theadvantage of allowing optimisation of the efficiency of the micromotor36 relative to the surface of the plate 30 which is used, andoptimisation of the surface of crystalline or amorphous material whichis used in order to produce the micromotors 36 and the driving modules13. Hence when the plate 30 is produced from a silicon wafer 101, asshown schematically in FIG. 10, the “V” shape allows interleavedreplication of the plates 30 on the surface of the wafer in order tomaximise the number of micromotors 36 obtained from a given siliconsurface. In particular, according to the example represented in FIG. 10,the plates 30 can be arranged on the wafer in parallel columns in themanner of chevrons, two columns Cn, Cn+1 which are adjacent beingorientated in the opposite direction. Furthermore, two adjacent plates30 of two adjacent columns Cn, Cn+1 have their lateral adjacent portions102 which are aligned.

Preferably, the angle described by the two actuators 38, 40 is betweenninety and one hundred and forty degrees. The greater is the angle, themore the interleaving of the plates 30 on the wafer 100 is optimised,but large angles require displacing the styli 44, 46 of the actuators38, 40 relative to their respective axes of symmetry A1, A2, whichimpairs the mechanical effectiveness of the actuators 38, 40.

According to the embodiment represented in the Figures, the casing 12which contains the driving module 13 comprises a lower plate 106provided in order to be fixed on an element of the timepiece 10, here onthe plate 12 of the movement, and the plate 30 of the driving module 13is mounted on the lower plate 106. The casing 12 comprises a protectivecap 108 which covers the driving module 13 which is fixed on the lowerplate 106, here by means of a screw 109, and which retains the drivingmodule 13 against the lower plate 106.

The upper face of the lower plate 106 comprises here a hollow or housing110 in which the plate 30 of the driving module 13 is received in asubstantially complementary manner.

The cap 108 comprises an open notch 112 in one of its exteriorperipheral edges and the pinion 62 is accommodated in this notch 112after assembly of the cap 108 on the lower plate 106.

Advantageously, a printed circuit 114 is intercalated between the lowerplate 106 and the cap 108 in order to allow electrical connection of themicromotor 36, via its pads 56, 57, 58, 59 to the electronic module ofthe timepiece 10.

According to an embodiment variant (not represented), the driving module13 can be mounted directly on the plate 26 which makes it possible todispense with the casing 12, in particular to minimise the number ofcomponents, in order to facilitate the assembly of the movement 27 andin order to minimise the spatial requirement of the driving means. Aprotective element can be provided on the driving module 13 in order toprotect its components.

1. An arrangement for mechanical interfacing of a micromotor of theMicro Electro Mechanical System type with a toothed wheel, thearrangement comprises: (i) a toothed wheel; (ii) a central shaftdefining a central axis; (iii) a micromotor, produced in an upper layerof a plate made of crystalline or amorphous material, wherein themicromotor comprises at least one linear actuator; (iv) a rotor,arranged above the plate, wherein the rotor is driven in rotation by theat least one linear actuator; (v) a pinion coaxial with the rotor andarranged above the rotor, wherein the rotor is disposed to rotate aboutthe central axis, wherein the rotor and the pinion are connected inrotation by at least one off-set pin that is received in an associatedhole formed in the rotor so as to be disposed off a center of the rotor,wherein operating play is provided between the rotor and the pinion sothat the rotor and the pinion are coupled in rotation angularly, saidoperating play including a radial clearance so that the rotor and thepinion move independently in a radial direction with respect to the axisof the central shaft, and wherein the pinion meshes with the toothedwheel.
 2. The arrangement according to claim 1, wherein the rotorcomprises a plurality of holes formed therein and distributed angularlyin a regular manner about an axis of rotation of the rotor, and whereinthere is an off-set pin associated with each hole, and the off-set pinsare integral with the pinion, wherein the radial clearance is providedby clearance between surfaces forming the plurality of holes in therotor and the off-set pins of the pinion.
 3. The arrangement accordingto claim 2, wherein each hole of the plurality of holes has a length anda width, wherein the length is greater than the width, and the length isoriented in a radial direction with respect to the axis of the centralshaft.
 4. The arrangement according to claim 2, wherein the pins areproduced in a single piece with the pinion.
 5. The arrangement accordingto claim 2, wherein each pin is received in the associated hole withboth radial and circumferential play.
 6. The arrangement according toclaim 1, wherein the upper layer of the plate comprises at least onesupport surface orientated towards a top of the plate and the pinion isdisposed to abut against the at least one support surface, and is thusprevented from coming to abut axially against the rotor, when an axialforce orientated towards a bottom of the plate is applied to the pinion.7. The arrangement according to claim 1, wherein the rotor is guided inrotation by the central shaft.
 8. The arrangement according to claim 7,wherein the rotor is guided in rotation by the same shaft as the pinion.9. The arrangement according to claim 1, wherein the pinion meshes withthe toothed wheel in a meshing zone situated close to an exteriorcircumferential edge of the plate.
 10. The arrangement according toclaim 9, wherein the rotor is driven in rotation by the actuator bymeans of a pawl and wherein the ratcheting zone is offset angularlyrelative to the meshing zone.
 11. The arrangement according to claim 1,wherein the hole is formed as a slot.
 12. A timepiece comprising anarrangement according to claim 1 mechanically interfacing the toothedwheel of a gear-train of the timepiece with the micromotor of thetimepiece.